[Diesel_Dave]

It's all the same data, just plotted vs. different independent variables.

Like I said, it's not really a controlled test because all those factors are changing at the same time. Additionally, some of the factors are correllated. For example, the weather has been getting warmer, so the later dates tend to have higher temps.

I haven't done it yet, but there may be a way to "adjust" for different factors. For example, I could scale the number around according to date (so that the slope of mpg vs day = 0), and then re-plot. Then again, that would also inherently skew some of the othe factors which happend to change with the day.

IMO, the most interesting thing to look at are the R2 values. Plots with higher R2 values mean there is a stronger correlation. For example, you can see there is a stroger correleation between temperature and mpg than there is humidity and mpg. Therefore, I would conclude that temperature is more signifcant than humidity. Of course, the slope matters too...